OFFSET
1,1
COMMENTS
An approximation to Pi.
FORMULA
Equals (1/2)*Sum_{k>=0} 2^(k-binomial(k,2)). - Andrew Howroyd, Feb 21 2020
Equals A190405 +2.5 = A299998 +1.5. All digits the same but the first one or two. - R. J. Mathar, Mar 10 2020
EXAMPLE
3.1416325606551538662938427702254294342260615379567...
MAPLE
c:= sum(2^(j*(3-j)/2-1), j=0..infinity):
evalf(c, 125); # Alois P. Heinz, Mar 03 2020
PROG
(PARI) suminf(k=0, 2^(k-binomial(k, 2)-1)) \\ Andrew Howroyd, Feb 21 2020
CROSSREFS
KEYWORD
nonn,cons
AUTHOR
Drew Edgette, Feb 19 2020
STATUS
approved